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It started how most ridiculous things in the Kingdom of Science did - with Gen.
Senku had spent the last several days troubleshooting, testing, and refining schematics for their next big project, having barely slept more than a few hours and skipping most of his meals.
“Eat.”
“Later.”
Gen shoved the spoon of now lukewarm stew against his mouth, smearing it up his cheek as Senku batted him away. “Now.”
Senku looked up at him, the dark circles under his eyes testament to the hours he’d spent laboring, and the irritated scowl on his face sure to scare off those with weaker constitutions than Gen’s. “I just have to finish this latest schematic and explain it to Kaseki-”
“You can do that tomorrow,” Gen insisted, a scowl of his own pulling at the corners of his mouth. “Now you’re going to eat a decent meal, take a bath, and get some sleep.”
Scoffing, Senku rubbed the back of his hand against his face to finally wipe away the smudged food, licking it off and wiping the residue on his tunic. “What are you, my mother?”
Before Gen could respond, the flap over the door whipped open, Chrome rushing in with an excited flush to his face and a chunk of rock cupped in his palms.
“Senku, you gotta see this rock I found, it’s totally bad!”
“Chrome, you better not leave all this crap out here expecting me to clean it up!” Kohaku followed behind, Suika trailing after her.
“I’ll take care of it, chill out, would ya?”
“Chill out?! You ran off and left Suika all alone, you’re lucky I was there!”
The little girl clutched at Kohaku’s skirt in a panic. “Suika was fine! Don’t fight!”
“We’re not fighting, Suika-”
“Oh, we’re gonna fight, Chrome, don’t you worry-”
Gen closed his eyes and took a deep breath as the trio continued to talk over one another, volume steadily rising. Glancing over at Senku, his mood soured further - the scientist’s fists had clenched, eyes unseeing as the left one twitched slightly, nostrils flaring and shoulders tense. His knee was slowly bouncing and if Gen could actually read minds he was sure he would hear him counting, in fact he could just picture Senku’s voice-
What are you, my mother?
With a flash of inspiration, Gen clapped his hands, cupping them together for the maximum noise on impact. The sharp sound silenced the bickering trio and turned their attention to him, and based on their expressions he was sure the smile on his face had overshot saccharine by a mile and landed in Stepford territory.
“Now, now, children, Mommy and Daddy need a few minutes of quiet to inish-fay the discussion they were having if you wouldn’t mind going back outside.”
Nobody moved, the charcoal pencil in Senku’s already clenched fist snapping in his grip. “Haaaa?”
Chrome’s mouth worked uselessly for a moment or two. “Are you… did you just say mommy and daddy?”
“Which one is the mom?” Suika asked Kohaku, her attempts at whispering failing as Gen’s attention pivoted to her.
“Obviously Senku-chan is the brilliant grumpy daddy who does the hard work to provide for us all, which makes me the doting mommy keeping all of you rebellious children in line.” He patted Suika’s melon helmet softly, tone light despite the thread of irritation he struggled to mask.
Kohaku snorted, “This is some weird sex thing, isn’t it?”
“First, no it’s not,” Senku pointed an aggressive finger in Kohaku’s direction, eyes flaming and ears red with embarrassment, before turning the finger to Gen. “Second, knock it off.”
Gen pouted theatrically, cupping his jaw and screwing up his eyebrows despondently, “Daddy shouldn’t be so ean-may to me in front of the children, we want to set a good example for their future relationships.” A sly smile crossed his face and he peered at Senku through the corners of his eyes, gaze steely, “As well as a good example for proper self care, like eating dinner and getting some sleep.”
Senku scowled, staring Gen down, teeth clenching at the way the mentalist stared back, his smile all teeth.
“Don’t we, Daddy ?”
Realizing Gen wasn’t going to back down, he narrowed his eyes and reached for the bowl of stew, shoveling a spoonful into his mouth. His expression shifted slightly, eyes widening and head jerking as if to say “ Happy now?”
“Wonderful. Was that really so ard-hay?”
Senku chewed like it was .
Suika tugged on Gen’s sleeve, drawing his attention back to her. “If you’re the mom and Senku’s the dad, does that make Kohaku Suika’s big sister?”
“Exactly,” he booped her nose affectionately as she giggled, turning to cling to Kohaku's leg with a cheer.
“Then I’m… the big brother?” Chrome still sounded very confused, brows knit as he tried to picture the family tree in this odd scenario.
Gen smirked, “You’re the family pet.”
Chrome squawked in disapproval, ready to argue when Senku spoke up. “If you're done reconstructing a family sitcom, I was in the middle of something.”
“Yes, eating dinner,” Gen replied, the saccharine smile back on his face but not reaching his eyes which glared down at Senku sternly. “You can get back to work after you finish and take a bath.”
“And after you sleep,” Kohaku added, arms crossed over her chest.
“Gen’s right, you do need a bath, dude,” Chrome piped in, grimacing slightly.
“But you have to eat your dinner first!” Suika chimed in, proud to be helpful.
Senku stared at them all before deflating, shoveling another spoonful of stew into his mouth with a huff.
“See? It’s so much easier when Daddy just does what Mommy tells him, isn’t it?”
“Don’t call me that,” Senku muttered, scowling at his bowl as it obviously fell on deaf ears.
Taking another bite, he sighed - maybe if he listened just this once, they’d knock it off.
—
They didn’t knock it off.
If anything, the fact that it ruffled Senku’s feathers the way it did only kept the shtick going longer. Over the next few weeks it spread amongst the rest of the Kingdom of Science, like a fungal infection or a horribly contagious chaos disease.
Suika started drawing “family portraits” of color coded stick figures, her wobbly handwriting labeling each member with their new titles and Gen proudly hanging them on the walls of the lab as if they were the doors of a refrigerator.
Kohaku began referring to them as “Mama-Gen and Papa-Senku” and Chrome as “the stray dog we adopted” to which Chrome would insist that he was actually the middle child and “honored heir to the Science Kingdom, thank you”.
Kaseki had begun calling Gen “mother” unironically, and even Ginro and Kinro had begun to play along, Ginro referring to Senku as a “cruel and unjust father” when assigned a particularly grueling task and Kinro playing the role as dutiful eldest brother supporting Gen’s directions to the others.
And, of course, any time Senku argued or protested, Gen would just smile with the smug satisfaction of someone who had gotten their way and would continue to do so no matter how Senku struggled.
So, Senku stopped struggling.
It started small - one afternoon Chrome poked into the lab to ask him if there was any spare soap he could use and Senku, without looking away as he slowly dripped a pipette into a waiting flask, muttered a “Go ask your mother.”
There was a beat of silence. “...You mean Gen?”
“Did I stutter?”
Chrome blinked, snorted, and stepped out of the lab, “ Moooooom?”
Several moments later Gen appeared in the doorway, smiling skeptically and eyebrow arched in disbelief, “Really?”
Senku had moved to the next flask, watching the mixture carefully as he added another two drops, swirling it slowly and shrugging. “I’m busy, you know where we keep that stuff.” When the color changed as he expected, he looked up and smirked, “Mother knows best, right?”
Gen huffed, rolling his eyes but Senku didn’t miss the fond tilt to his smile as he turned to leave, “And don’t you forget it, Daddy .”
From there it spiraled.
“Did you ask your mother?” Senku would say when someone came to him with a non-technical question. When tasks were delegated and someone tried to argue, Gen would beam, “Listen to your father.”
Chrome would whine theatrically when Gen ordered them to bed for the night, grinning wide as he begged for just “ five more minutes, mom” , and Ginro would snicker at the put-upon look Gen would get when he told him that “ Daddy didn’t eat lunch today” and the resulting glower Senku directed at him for being sold out.
Gen would send Suika to “fetch daddy for dinner” knowing Senku had a harder time resisting her requests, and Senku would task Kohaku and Kinro to “make sure mom doesn’t get lost scavenging the woods”.
It was a few weeks later when Senku looked up from his tinkering to find Gen asleep on his bedroll, Senku’s rolled out and waiting for when the scientist inevitably dragged himself to bed. He reached for the thermos of tea Gen had left on his worktop before turning in for the night, taking a sip when it hit him.
This was nice .
Quiet domesticity. Casual teamwork. Shared meals, bickering over chores, the warm presence of another person always in his peripherals.
He couldn’t remember the last time someone injected themselves into his space without throwing him off balance. Gen just… fit. Dramatic and ridiculous but somehow the perfect support to keep the Kingdom of Science running and Senku from pushing himself to failure.
A week later, Gen kissed him.
It wasn’t planned.
Senku was gathering things from the lab for a supply trip with Chrome, loading a bag and ticking things off a list as Gen watched from his place leaning against the door frame.
“Do come back in one piece, Senku-chan, I’d never forgive you if you left me a single mother.”
Senku grunted, hoisting the bag onto his shoulder, “Yeah, yeah, you act like we're crossing the desert and not digging through the same cave for the hundredth time…”
Gen chuckled, “In that case, have un-fay at work, Daddy.”
And with that he stepped forward and gave Senku a quick kiss on the cheek.
Senku froze.
Gen realized what he had done a beat later. “Oh- I just… I didn’t mean…”
Senku stared at him, the spot on his cheek warm and almost tingling. He thought about cups of tea, lectures to eat, a bedroll left out for him.
“I don’t mind.”
“What?”
Senku cleared his throat, sure his cheeks were flushing. “I don’t mind... wouldn't mind if you did it again. If you wanted to. ”
Gen blinked, lips parting, and Senku didn’t meet his gaze, adjusting the strap of his bag with exaggerated focus and pretending to read something off the checklist he’d long since memorized and completed.
“You don't mind... the joke? Or..."
Senku made a noncommittal noise, "Both. Either." He looked up as Gen stepped closer, tentative this time, gaze unsure but the smile on his face soft. “It's fine if it's you.”
When Gen kissed him again, slow and unhurried, Senku didn’t freeze. He leaned in just enough, a gentle press back, kissing back instead of just being kissed.
It wasn’t long, but when Gen pulled back he was smiling that impossibly fond way he sometimes did when Senku did something uncharacteristically nice. The way that made Senku puff up with pride but feel a little self-conscious, ears heating up.
He looked away, “Chrome’s waiting,” he muttered, voice low but warm.
Gen hummed, reaching up to brush a strand of hair away from Senku’s face, touch gentle as it brushed the top of his ear causing Senku to shiver. “Can’t keep the children waiting, can we?” He laughed softly as Senku rolled his eyes, tapping the reddened skin on the shell of his ear once more. “Go on, daddy, I can take care of things here while you’re gone.”
“I know you can,” Senku replied easily, using a burst of confidence to press another kiss to Gen’s lips before turning to disguise the blush he knew had spread across his face, hurrying out of the lab.
Gen watched him go, fingers pressed to his lower lip thoughtfully before he heard Senku’s voice cross the camp and dissolved into laughter.
“ You kids better listen to your mother while I’m gone!”
–
That night, Senku returned far after the sun set, mud on his boots and an array of new materials to sort through and catalogue. His bedroll was there again, already laid out next to Gen’s where the mentalist slept soundly, several inches closer than it had been the previous nights.
A thermos of tea waited on the worktable, still warm.
He set his bag down and drank the tea, walking past without pause to ready himself for bed. Laying down, he listened to the soft even breaths next to him, and felt the warmth radiating from the body so close. In the soft moments as he felt sleep drifting over him, he reached out and curled his fingers around the lax ones resting next to Gen.
He'd always known that family wasn’t defined by blood, but for the first time since he’d woken up from the stone, he finally felt he was home .
And better yet, he had someone to share it with.